Clinical Side Effects of Phenobarbital, Primidone, Phenytoin, Carbamazepine, and Valproate During Monotherapy in Children

The rate of onset of side effects was examined in 392 pediatric outpatients who received long-term monotherapy with phenobarbital (PB), primidone (PRM), phenytoin (PHT), carbamazepine (CBZ), or valproate (VPA) for epilepsy or febrile convulsions. The severity of side effects (based on need to alter treatment), the nature of each drug's most common side effects, and the doses and plasma levels of occurrence were recorded. Our results show that usually accepted therapeutic ranges are well tolerated. Indeed, although some form of side effect occurred in 50% of patients, treatment had to be changed in only 18% and the drug had to be stopped in only 7%. In decreasing order, the rates for side effects were PHT (71%) greater than PB (64%) greater than CBZ (43%) greater than VPA (43%) greater than PRM (29%). Serious side effects requiring withdrawal of treatment occurred at the following rates: PHT (10%) greater than VPA (8%) greater than PRM (8%) greater than PB (4%) greater than CBZ (3%). Among our patients, the best tolerated antiepileptic drug (AED) was CBZ, and the least tolerated was PHT. Behavioral disorders were most common with PB, neurologic disorders with PHT, digestive tract disorders with VPA, and gingival hyperplasia and hirsutism with PHT. Behavioral disorders involving excitement seen with PB and PRM occurred most commonly at low plasma levels. Behavioral disorders involving depression seen with PB and VPA, those involving excitement seen with PHT and VPA, and digestive disorders seen with VPA occurred particularly when plasma levels were high.